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fix triangle() orientation in webgl mode #6263

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merged 2 commits into from
Jul 10, 2023
Merged

fix triangle() orientation in webgl mode #6263

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4cc80ca
fix triangle orientation
inaridarkfox4231 Jul 10, 2023
9a6261e
add explanation comments
inaridarkfox4231 Jul 10, 2023
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4 changes: 3 additions & 1 deletion src/webgl/3d_primitives.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1070,10 +1070,12 @@ p5.RendererGL.prototype.triangle = function(args) {
// origin appropriately.
const uMVMatrix = this.uMVMatrix.copy();
try {
// triangle orientation.
const orientation = Math.sign(x1*y2-x2*y1 + x2*y3-x3*y2 + x3*y1-x1*y3);
const mult = new p5.Matrix([
x2 - x1, y2 - y1, 0, 0, // the resulting unit X-axis
x3 - x1, y3 - y1, 0, 0, // the resulting unit Y-axis
0, 0, 1, 0, // the resulting unit Z-axis (unchanged)
0, 0, orientation, 0, // the resulting unit Z-axis (Reflect the specified order of vertices)
x1, y1, 0, 1 // the resulting origin
]).mult(this.uMVMatrix);

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